Acoustic waveguide assemblies

ABSTRACT

Acoustic waveguides are disclosed for mounting to a conduit. The acoustic waveguides provide a mounting area that minimizes the effect of the mount on the acoustic wave traveling through the waveguide while providing an effective seal, even under high pressure conditions.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to acoustic waveguideassemblies for mounting an acoustic waveguide to a conduit.

Acoustic waveguides can be used to measure the characteristics (e.g.,density, viscosity, level, temperature, etc.) of a fluid traveling in aconduit using acoustic waves. In a typical acoustic waveguide, atransducer assembly launches an acoustic wave into a waveguide that ismounted and sealed to the conduit and inserted into the fluid. The timeof flight of the acoustic wave in the section of the waveguide insertedinto the fluid is a function of the characteristics of the fluid andtherefore can be used to determine those characteristics.

Some acoustic wave types require that the waveguide be a thin elongatedrod. One of the limitations of these thin elongated rods that preventuse in most commercial and industrial applications, especially in highpressure installations, is the difficulty of mounting and sealing thewaveguide to the conduit in a way that will not significantly affect theacoustic wave as it passes through the waveguide in the area of theseal. Sealing with an o-ring around the thin elongated rod of thewaveguide is also difficult, especially in high pressure installations.While seals made of polytetrafluoroethylene (PTFE) have been used inlaboratory settings, those seals are not sufficient for long term useunder high pressure as the seals can deform over time and fail.

The discussion above is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

BRIEF DESCRIPTION OF THE INVENTION

Acoustic waveguide assemblies are disclosed for mounting an acousticwaveguide to a conduit. The acoustic waveguide assemblies provide amounting area that minimizes the effect of the mount on the acousticwave traveling through the acoustic waveguide while providing aneffective seal, even under high pressure conditions. An advantage thatmay be realized in the practice of some disclosed embodiments of theacoustic waveguides is allowing the use of thin elongated waveguides formore accurate density measurements that can provide more accurate flowmeasurements.

In one exemplary embodiment, an acoustic waveguide assembly for mountingto a conduit is disclosed. The acoustic waveguide comprises a waveguiderod having a proximal end and a distal end, a waveguide sensor connectedto the distal end of the waveguide rod, and a tube couplercircumferentially surrounding a portion of the waveguide rod, whereinthe tube coupler provides a surface to mount the waveguide rod to theconduit.

In another exemplary embodiment, the acoustic waveguide comprises awaveguide rod having a proximal end and a distal end, a waveguide sensorconnected to the distal end of the waveguide rod, and a disk couplercircumferentially surrounding a portion of the waveguide rod, whereinthe disk coupler provides a surface to mount the waveguide rod to theconduit.

This brief description of the invention is intended only to provide abrief overview of subject matter disclosed herein according to one ormore illustrative embodiments, and does not serve as a guide tointerpreting the claims or to define or limit the scope of theinvention, which is defined only by the appended claims. This briefdescription is provided to introduce an illustrative selection ofconcepts in a simplified form that are further described below in thedetailed description. This brief description is not intended to identifykey features or essential features of the claimed subject matter, nor isit intended to be used as an aid in determining the scope of the claimedsubject matter. The claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in thebackground.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features of the invention can beunderstood, a detailed description of the invention may be had byreference to certain embodiments, some of which are illustrated in theaccompanying drawings. It is to be noted, however, that the drawingsillustrate only certain embodiments of this invention and are thereforenot to be considered limiting of its scope, for the scope of theinvention encompasses other equally effective embodiments. The drawingsare not necessarily to scale, emphasis generally being placed uponillustrating the features of certain embodiments of the invention. Inthe drawings, like numerals are used to indicate like parts throughoutthe various views. Thus, for further understanding of the invention,reference can be made to the following detailed description, read inconnection with the drawings in which:

FIG. 1 is perspective view of an exemplary acoustic waveguide;

FIG. 2 is a cross-section of another exemplary acoustic waveguide with atube coupler for mounting the acoustic waveguide to a conduit;

FIG. 3 is a cross-section of the portion of the exemplary acousticwaveguide of FIG. 2 showing the tube coupler;

FIG. 4 is a cross-section of an exemplary acoustic waveguide assemblyfor mounting the acoustic waveguide of FIG. 2 to a conduit through anozzle;

FIG. 5 is a cross-section of another exemplary acoustic waveguideassembly for mounting the acoustic waveguide of FIG. 2 to a conduit in amiddle flange;

FIG. 6 is a cross-section of yet another exemplary acoustic waveguideassembly for mounting the acoustic waveguide of FIG. 2 to a conduitusing a compression fitting in a flange;

FIG. 7 is a perspective view of yet another exemplary acoustic waveguidewith a disk coupler for mounting the acoustic waveguide to a conduit;

FIG. 8 is a cross-section of an exemplary acoustic waveguide assemblyfor mounting the acoustic waveguide of FIG. 7 to a conduit through anozzle;

FIG. 9 is a perspective view of still another exemplary acousticwaveguide with a disk coupler for mounting the acoustic waveguide to aconduit;

FIG. 10 is a cross-section of an exemplary acoustic waveguide assemblyfor mounting the acoustic waveguide of FIG. 9 to a conduit through anozzle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of an exemplary acoustic waveguide 10. Inone embodiment, a transducer assembly 2 is coupled to the proximal endof a waveguide rod 4. The distal end of the waveguide rod 4 can connectto a waveguide sensor 6, which is the portion of the acoustic waveguide10 that will be submerged in the fluid. The transducer assembly 2 cancomprise two transducers on opposite sides of the waveguide rod 4 and beconfigured to launch an acoustic wave into the acoustic waveguide 10.Each of the transducers can comprise a piezoelectric crystalencapsulated by packaging, or in another embodiment, only comprise thepiezoelectric crystal.

In different embodiments, the mounting locations of the transducers onthe waveguide rod 4, mounting angles of the transducers with respect tothe longitudinal axis of the waveguide rod 4, polarity of thetransducers, and the excitation pulse received by the transducers can bemodified to launch particular acoustic waves (e.g., ultrasonictorsional, extensional, flexural waves) into the waveguide rod 4.Although the exemplary acoustic waveguides disclosed herein will bedescribed with respect to use with torsional waves, it will beunderstood that the waveguides can be used for different acoustic waves.

An ultrasonic torsional wave is a wave motion in which the vibrations ofthe medium are periodic twisting motions around the direction ofpropagation along the azimuthal direction of the torsional waveguide.For use with torsional waves, the waveguide rod 4 can be a thin (e.g.,0.25 in. diameter (6.35 mm) for a 100 kHz wave, 0.375 in. diameter (9.53mm) for a 75 kHz wave, 0.50 in. diameter (12.70 mm) for a 50 kHz wave),elongated rod having a circular cross-section into which the transducerassembly 2 launches the ultrasonic torsional wave. The waveguide sensor6 can be a thin, elongated non-circular cross-section (e.g., diamondshaped), which is submerged in the fluid. When the ultrasonic torsionalwave traveling down the waveguide rod 4 hits the interface between thewaveguide rod 4 and the waveguide sensor 6, the ultrasonic torsionalwave is partially reflected at the interface back to the transducerassembly 2 providing a first time of flight measurement, while theremainder of the ultrasonic torsional wave will transmit through thewaveguide sensor 6. When the remainder of the ultrasonic torsional wavehits the end of the waveguide sensor 6, the ultrasonic torsional wavewill reflect back to the transducer assembly 2, providing a second timeof flight measurement. The time of flight in the waveguide sensor 6depends, in part, upon the density of the fluid, with a slower time offlight for more dense fluids and a faster time of flight for less densefluids. The slow speed of the ultrasonic torsional wave in the waveguidesensor 6 provides high sensitivity to changes in the density of thefluid surrounding that section of the acoustic waveguide 10. Knowledgeof the actual density of a fluid, along with traditional transit time orDoppler measurements that can only provide flow velocity, can providemore accurate mass flow measurements than measurements using acalculated density based on temperature and pressure of the fluid.

FIG. 2 is another exemplary acoustic waveguide 100 with a tube coupler110 for mounting the acoustic waveguide 100 to a conduit 50 (see FIGS.4, 5, and 6). Although the figures show the exemplary acousticwaveguides mounted to a pipe, it will be understood that the acousticwaveguides can be mounted to a variety of conduits in which fluidtravels (e.g., a pipe, tube, vessel, tank, etc.). FIG. 3 is across-section of a portion of the exemplary acoustic waveguide 100 ofFIG. 2 showing the tube coupler 110. In one embodiment, a transducerassembly 102 is coupled to the proximal end of the waveguide rod 104,which can have a circular cross-section. The distal end of the waveguiderod 104 can connect to a waveguide sensor 106, which is the portion ofthe acoustic waveguide 100 that will be submerged in the fluid and canhave a non-circular cross-section.

The tube coupler 110 circumferentially surrounds a portion of thewaveguide rod 104 to provide a surface for mounting the acousticwaveguide 100 to a conduit 50. The exemplary tube coupler 110 comprisesa first end 114 (e.g., a flat or curved disk) circumferentiallysurrounding the waveguide rod 104 at a first location and a second end115 (e.g., a flat or curved disk) circumferentially surrounding thewaveguide rod 104 at a second location. The tube coupler 110 alsocomprises an inner sleeve 112 circumferentially surrounding thewaveguide rod 104 and extending from the first end 114 to the second end115 proximate the waveguide rod 104. In one embodiment, the inner sleeve112 is not fixedly attached to the waveguide rod 104 to minimize contactbetween the tube coupler 110 and the waveguide rod 104 to avoiddampening of the acoustic waves traveling through the waveguide rod 104.For example, the inner sleeve 112 can form a close sliding fit with thewaveguide rod 104 without applying pressure on the waveguide rod 104.The inner sleeve 112 can be made of a material different than thewaveguide rod 104 that has a different acoustic impedance than thewaveguide rod 104 to provide acoustic isolation between the waveguiderod 104 and the tube coupler 110.

The tube coupler 110 can further comprise an outer tube 116circumferentially surrounding the inner sleeve 112 and extending fromthe first end 114 to the second end 115, forming a cavity 118 betweenthe inner sleeve 112 and the outer tube 116. The tube coupler 110 canhave varying lengths to provide the desired acoustic performance of theacoustic waveguide 110. The cavity 118 can be filled with filler (e.g.,a liquid or a non-metallic solid (e.g., epoxy)) that can providemechanical support for the second end 115, which provides a boundaryagainst the pressure in the conduit 50 (see FIGS. 4, 5, and 6). Inaddition to providing mechanical support, the filler can be chosen toprovide acoustic isolation between the waveguide rod 104 and the tubecoupler 110.

The first end 114 and the second end 115 of the tube coupler 110 can berelatively thin (e.g., 0.007 in. (0.178 mm) to 0.010 in. (0.254 mm). Thefirst end 114 and second end 115 can be welded to the waveguide rod 104,while the inner sleeve 112 and the outer tube 116 can be welded to thefirst end 114 and the second end 115. The components of the tube coupler110 may be made of corrosion resistant materials (e.g., stainless steel316, titanium, graphite) and welded together using different weldingtechniques, including, e.g., groove welding, fillet welding, resistancewelding, e-beam welding, friction welding, or brazing.

FIG. 4 is a cross-section of an exemplary acoustic waveguide assembly120 for mounting the acoustic waveguide 100 of FIG. 2 to a conduit 50through a nozzle 122. The transducer assembly 102 can be mounted to thewaveguide rod 104 using a clamp 124 (e.g., a T-clamp). The clamp 124 canbe spring loaded to provide the necessary contact pressure between thetransducer assembly 102 and the waveguide rod 104 to ensure propertransmission of the acoustic wave into the waveguide rod 104. A nozzle122 provides a port 123 for accessing the fluid inside of the conduit50. Although the nozzle 122 and the port 123 are shown to be orientedperpendicular to the conduit 50 and the direction of flow 60 of thefluid in FIG. 4, it will be understood that the orientation can be atdifferent angles or locations on the conduit 50 (e.g., horizontal,vertical, elbow, angled). The tube coupler 110 can be inserted into theport 123 of the nozzle 122 such that the waveguide sensor 106 extendsinto the fluid flowing in the conduit 50. The length of the waveguidesensor 106 can be the same as the inner diameter of the conduit 50,recessed in the port 123 of the nozzle 122, or mounted flush with theinner diameter of the conduit 50. As shown in FIG. 4, the tube coupler110 forms a seal of the port 123 of the nozzle 122 and therefore mustwithstand the pressure in the conduit 50. The second end 115 and thefiller in the cavity 118 (see FIG. 3) of the tube coupler 110 providethe mechanical support to withstand the pressure in the conduit 50. Inaddition, an o-ring (not shown) can be installed in the port 123 of thenozzle 122 proximate the outer tube 116 of the tube coupler 110 (seeFIG. 3) to further seal the port 123. The tube coupler 110 can befixedly attached to the port 123 of the nozzle 122 by, e.g., welding orthreading.

FIG. 5 is a cross-section of another exemplary acoustic waveguideassembly 130 for mounting the acoustic waveguide 100 of FIG. 2 to aconduit 50 in a flange. A first section of the conduit 50 terminating ina first flange 52 is coupled to a second section of the conduit 50terminating in a second flange 54 through a middle flange 56 by aplurality of bolts 53 extending through the first flange 52, the secondflange 54, and the middle flange 56. The middle flange 56 provides aport 57 for accessing the fluid inside of the conduit 50. The tubecoupler 110 can be inserted into the port 57 of the middle flange 56such that the waveguide sensor 106 extends into the fluid flowing in theconduit 50. As shown in FIG. 5, the tube coupler 110 forms a seal of theport 57 of the middle flange 56 and therefore must withstand thepressure in the conduit 50. In addition, an o-ring (not shown) can beinstalled in the port 57 of the middle flange 56 proximate the outertube 116 of the tube coupler 110 (see FIG. 3) to further seal the port57.

FIG. 6 is a cross-section of yet another exemplary acoustic waveguideassembly 140 for mounting the acoustic waveguide 100 of FIG. 2 to aconduit 50 using a compression fitting 142 in a flange. A first sectionof the conduit 50 terminating in a first flange 52 is coupled to asecond section of the conduit 50 terminating in a second flange 54through a middle flange 58 by a plurality of bolts 53 extending throughthe first flange 52, the second flange 54, and the middle flange 58. Themiddle flange 58 provides a port 59 for accessing the fluid inside ofthe conduit 50. The tube coupler 110 can be inserted into a compressionfitting 142, which is then inserted into the port 59 of the middleflange 58 such that the waveguide sensor 106 extends into the fluidflowing in the conduit 50. The port 59 of the middle flange 58 can beshaped to receive the compression fitting 142 (e.g., threaded to receivethe threads of the compression fitting 142). As shown in FIG. 6, thetube coupler 110 forms a seal of the port 59 of the middle flange 58 andtherefore must withstand the pressure in the conduit 50.

FIG. 7 is a perspective view of yet another exemplary acoustic waveguide200 with a disk coupler 210 for mounting the acoustic waveguide 200 to aconduit 50 (see FIG. 8). In one embodiment, a transducer assembly 202 iscoupled to the proximal end of the waveguide rod 204, which can have acircular cross-section. The distal end of the waveguide rod 204 canconnect to a waveguide sensor 206, which is the portion of the acousticwaveguide 200 that will be submerged in the fluid and can have anon-circular cross-section. The disk coupler 210 circumferentiallysurrounds a portion of the waveguide rod 204 to provide a surface formounting the acoustic waveguide 200 to a conduit 50. In one embodiment,the disk coupler 210 can be welded to the waveguide rod 204, while inanother embodiment, the disk coupler 210 can be integral with thewaveguide rod 204 if both are made by machining the same block ofmaterial.

FIG. 8 is a cross-section of an exemplary acoustic waveguide assembly220 for mounting the acoustic waveguide 200 of FIG. 7 to a conduit 50through a nozzle 222. The transducer assembly 202 can be mounted to thewaveguide rod 204 using a clamp 124 (e.g., a T-clamp). The clamp 124 canbe spring loaded to provide the necessary contact pressure between thetransducer assembly 202 and the waveguide rod 204 to ensure propertransmission of the acoustic wave into the waveguide rod 204. A nozzle222 provides a port 223 for accessing the fluid inside of the conduit50. Although the nozzle 222 and the port 223 are shown to be orientedperpendicular to the conduit 50 and the direction of flow 60 of thefluid in FIG. 8, it will be understood that the orientation can beatdifferent angles or locations on the conduit 50 (e.g., horizontal,vertical, elbow, angled). The bottom side of disk coupler 210 can bemounted on the outlet 225 of the port 223 of the nozzle 222 such thatthe waveguide sensor 206 extends through the port 223 into the fluidflowing in the conduit 50. The disk coupler 210 is mounted between a topflange 224 on the top side of the disk coupler 210 and the nozzle 222with a plurality of bolts 228 extending through the top flange 224 andthe nozzle 222. As shown in FIG. 8, the disk coupler 210 forms a seal ofthe port 223 of the nozzle 222. In addition, a first gasket 226 can beinstalled between the top surface of the disk coupler 210 and the topflange 224. A second gasket 227 can be installed between the bottomsurface of the disk coupler 210 and the outlet 225 of the port 223 ofthe nozzle 222 to further seal the port 223.

FIG. 9 is a perspective view of still another exemplary acousticwaveguide 300 with a disk coupler 310 for mounting the acousticwaveguide 300 to a conduit 50 (see FIG. 10). The distal end of thewaveguide rod 304 can connect to a waveguide sensor 306, which is theportion of the acoustic waveguide 300 that will be submerged in thefluid and can have a non-circular cross-section. The disk coupler 310circumferentially surrounds a portion of the waveguide rod 304 toprovide a surface for mounting the acoustic waveguide 300 to a conduit50. In one embodiment, the disk coupler 310 can be welded to thewaveguide rod 304, while in another embodiment, the disk coupler 310 canbe integral with the waveguide rod 304 if both are made by machining thesame block of material. In still another embodiment, the disk coupler310 can be coupled to the waveguide rod 304 using mating threads on eachpart.

As shown in FIG. 9, the transducer assembly 302 is coupled to thecircumference of the disk coupler 310. The transducer assembly 302 canbe coupled to the disk coupler 310 using, e.g., an adhesive (epoxy) or acircumferential clamp. The transducer assembly 302 can comprise twotransducers on opposite sides of the disk coupler 310 and be configuredto launch an acoustic wave into the acoustic waveguide 300. Each of thetransducers can comprise a piezoelectric crystal encapsulated bypackaging, or in another embodiment, only comprise the piezoelectriccrystal.

FIG. 10 is a cross-section of an exemplary acoustic waveguide assembly320 for mounting the acoustic waveguide 300 of FIG. 9 to a conduit 50through a nozzle 322. The transducer assembly 302 can be coupled to thedisk coupler 310 to ensure proper transmission of the acoustic wave intothe waveguide rod 304. Coupling the transducer assembly 302 to the diskcoupler 310 eliminates the need for a transducer clamp and can minimizethe amount of acoustic signal lost through the disk coupler 310. Anozzle 322 provides a port 323 for accessing the fluid inside of theconduit 50. Although the nozzle 322 and the port 323 are shown to beoriented perpendicular to the conduit 50 and the direction of flow 60 ofthe fluid in FIG. 10, it will be understood that the orientation canbeat different angles or locations on the conduit 50 (e.g., horizontal,vertical, elbow, angled). The disk coupler 310 can be mounted on theoutlet 325 of the port 323 of the nozzle 322 such that the waveguidesensor 306 extends through the port 323 into the fluid flowing in theconduit 50. The disk coupler 310 is mounted between a top flange 324resting on top of the disk coupler 310 and the nozzle 322 with aplurality of bolts 328 extending through the top flange 324 and thenozzle 322. As shown in FIG. 10, the disk coupler 210 forms a seal ofthe port 323 of the nozzle 322. In addition, a first gasket 326 can beinstalled between the top surface of the disk coupler 310 and the topflange 324. A second gasket 327 can be installed between the bottomsurface of the disk coupler 310 and the outlet 325 of the port 323 ofthe nozzle 322 to further seal the port 323.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. An acoustic waveguide assembly for mounting to aconduit, the acoustic waveguide assembly comprising: an acousticwaveguide comprising a waveguide rod having a proximal end and a distalend, a waveguide sensor connected to the distal end of the waveguiderod, and a tube coupler circumferentially surrounding a portion of thewaveguide rod, wherein the tube coupler provides a surface to mount thewaveguide rod to the conduit; and a middle flange comprising a port foraccessing the inside of the conduit located between a first flangeterminating a first section of the conduit and second flange terminatinga second section of the conduit, wherein the tube coupler is insertedinto the port of the middle flange such that the waveguide sensorextends into the conduit.
 2. The acoustic waveguide assembly of claim 1,wherein the tube coupler comprises: a first end circumferentiallysurrounding the waveguide rod at a first location; a second endcircumferentially surrounding the waveguide rod at a second location; aninner sleeve circumferentially surrounding the waveguide rod andextending from the first end to the second end proximate the waveguiderod; and an outer tube circumferentially surrounding the inner sleeveand extending from the first end to the second end, forming a cavitybetween the inner sleeve and the outer tube.
 3. The acoustic waveguideassembly of claim 2, wherein the cavity is filled with a non-metallicsolid.
 4. The acoustic waveguide assembly of claim 2, wherein the cavityis filled with a liquid.
 5. The acoustic waveguide assembly of claim 2,further comprising a transducer assembly coupled to the proximal end ofthe waveguide rod.
 6. The acoustic waveguide assembly of claim 2,wherein the first end and the second end of the tube coupler are disks.7. An acoustic waveguide assembly for mounting to a conduit, theacoustic waveguide assembly comprising: an acoustic waveguide comprisinga waveguide rod having a proximal end and a distal end, a waveguidesensor connected to the distal end of the waveguide rod, and a tubecoupler circumferentially surrounding a portion of the waveguide rod,wherein the tube coupler provides a surface to mount the waveguide rodto the conduit; and a middle flange comprising a port for accessing theinside of the conduit located between a first flange terminating a firstsection of the conduit and second flange terminating a second section ofthe conduit, wherein the tube coupler is inserted into a compressionfitting that is inserted into the port of the middle flange such thatthe waveguide sensor extends into the conduit.
 8. The acoustic waveguideassembly of claim 7, wherein the tube coupler comprises: a first endcircumferentially surrounding the waveguide rod at a first location; asecond end circumferentially surrounding the waveguide rod at a secondlocation; an inner sleeve circumferentially surrounding the waveguiderod and extending from the first end to the second end proximate thewaveguide rod; and an outer tube circumferentially surrounding the innersleeve and extending from the first end to the second end, forming acavity between the inner sleeve and the outer tube.
 9. The acousticwaveguide assembly of claim 8, wherein the cavity is filled with anon-metallic solid.
 10. The acoustic waveguide assembly of claim 8,wherein the cavity is filled with a liquid.
 11. The acoustic waveguideassembly of claim 8, further comprising a transducer assembly coupled tothe proximal end of the waveguide rod.
 12. The acoustic waveguideassembly of claim 8, wherein the first end and the second end of thetube coupler are disks.
 13. An acoustic waveguide assembly for mountingto a conduit, the acoustic waveguide assembly comprising: an acousticwaveguide comprising a waveguide rod having a proximal end and a distalend, a waveguide sensor connected to the distal end of the waveguiderod, and a tube coupler circumferentially surrounding a portion of thewaveguide rod, wherein the tube coupler provides a surface to mount thewaveguide rod to the conduit; a first end circumferentially surroundingthe waveguide rod at a first location; a second end circumferentiallysurrounding the waveguide rod at a second location; an inner sleevecircumferentially surrounding the waveguide rod and extending from thefirst end to the second end proximate the waveguide rod; and an outertube circumferentially surrounding the inner sleeve and extending fromthe first end to the second end, forming a cavity between the innersleeve and the outer tube.
 14. The acoustic waveguide assembly of claim13, wherein the cavity is filled with a non-metallic solid.
 15. Theacoustic waveguide assembly of claim 13, wherein the cavity is filledwith a liquid.
 16. The acoustic waveguide assembly of claim 13, furthercomprising a transducer assembly coupled to the proximal end of thewaveguide rod.
 17. The acoustic waveguide assembly of claim 13, whereinthe waveguide rod has a circular cross-section.
 18. The acousticwaveguide assembly of claim 13, wherein the waveguide sensor has anon-circular cross-section.
 19. The acoustic waveguide assembly of claim13, wherein the first end and the second end of the tube coupler aredisks.
 20. The acoustic waveguide assembly of claim 19, wherein thedisks are curved.